Field of Invention
The invention relates to an optical device for scanning and/or creating an information track on an optically scannable information carrier, which device is provided with a radiation source and an optical system with an objective lens system for focusing a radiation beam originating from the radiation source on the information carrier, said optical system comprising at least one optical component which is accommodated in a holder and can be adjusted in the direction of its optical axis, said optical component being guidable along a guide provided on a frame.
The invention further relates to an optical player comprising a support for an optically scannable information carrier, which support can be rotated about an axis of rotation, an optical device for scanning and/or creating an information track on the information carrier, said optical device being provided with a radiation source and an optical system with an objective lens system for focusing a radiation beam originating from the radiation source on the information carrier, at least the objective lens system being displaceable, by means of a displacement device, with respect to the information carrier in a substantially radial direction relative to the axis of rotation, and the optical system comprising at least one optical component which is accommodated in a holder and can be adjusted in the direction of its optical axis, said optical component being guidable along a guide provided on a frame.
An optical device of the type mentioned in the opening paragraphs is well known because it is employed in large numbers in, for example, CD players for listening to music. Meanwhile, new applications of such optical devices are known, such as in CD ROM players for software and in DVD players for images and sound. In connection with the necessary high information density, DVD players are provided with a type of radiation source, in the form of a laser source, which differs from that used in the above-mentioned audio CD players and CD ROM players. Apart from scanning an information track on an information carrier, meanwhile such optical devices are also used to create an information track on an information carrier, which application is commercially available now. The optical device in accordance with the opening paragraph forms part of an optical player in accordance with said opening paragraph, wherein at least the objective lens system of the optical system can be radially displaced, i.e. at right angles to the information track, along a disc-shaped information carrier. As the information density on the information carrier increases, the accuracy with which the radiation beam has to be positioned on the information carrier and focused increases too. This applies, in particular, to the so-called DVD+RW standard. For this reason, it is important that all optical parts of the optical system are correctly positioned with respect to each other. This can be achieved by embodying at least one optical component of the optical system so as to be displaceable in the direction of its optical axis, so that the relevant component can be properly positioned, in the course of the manufacturing process, in the direction of its optical axis. Such adjustable optical components can be formed, for example, by a so-called collimator lens, a so-called beam shaper and/or a servo lens present between a so-called polarizing beam splitter (PBS) and a diode which converts an optical signal to an electrical signal. The functions of all these optical components will be explained in greater detail by means of the description of a preferred embodiment in accordance with the invention. To displace an optical component in the direction of its optical axis, use is made, in accordance with the prior art, of a tubular holder which is provided around the optical component and extends on either side of said component in the direction of the optical axis. In connection with the displaceability, a rail system is provided which is composed of two rod-shaped elements which are rigidly attached to the frame. The tube comprising, in its interior, said optical component can be displaced along the rail system. Such an embodiment is described in JP-A-11134694. Although said embodiment is comparatively insensitive to the risk of tilting, it still takes up much space. However, the available space is limited. This problem applies, in particular, to DVD players which should often also be suitable for traditional CDs having a comparatively limited information density. For this purpose, the optical device in accordance with the prior art is provided with a second optical system having a separate radiation source and a separate optical lens system.
It is an object of the invention to provide an optical device and an optical player of the types mentioned in the opening paragraphs, in which the adjustability of the optical components to be adjusted requires only a limited amount of space, and in which a high degree of stability of the position of the relevant component is obtained both during and after the adjusting of such a component. In addition, the optical component should not be liable to tilting during the adjusting operation, i.e. tilting about an axis extending perpendicularly to the optical axis.
To achieve this object, an optical device in accordance with the invention is characterized in that the holder comprises a rod-shaped guiding element extending parallel to the optical axis and on either side of the optical component, which rod-shaped guiding element is used to displace the optical element along the guide in order to set the optical component so as to be positioned in the direction of the optical axis.
To achieve this object, an optical player in accordance with the invention is characterized in that the optical device employed therein is an optical device in accordance with the invention.
It is to be noted that, within the framework of this invention, the expression xe2x80x9crod-shaped elementxe2x80x9d is to be taken to mean that this element, viewed in a direction parallel to the optical axis of this optical component, is elongated. The shape of the cross-section can be chosen freely, in principle, although certain shapes may be advantageous. In comparison with the tubular holder, the rod-shaped guiding element takes up substantially less space than the tubular holders in accordance with the prior art. In addition, the design of the holder with the rod-shaped guiding element may be such that the rod-shaped guiding element is situated on the side of the optical component where space is available.
In accordance with a preferred embodiment, the guiding element at least partly has a surface that is curved around its longitudinal axis. By virtue of this curved surface, a line contact is established between the guiding element and the guide of the frame. A line contact is more favorable than a surface contact because a line contact is better defined and causes less friction during displacement.
Preferably, only at the end portions the guiding element is in guiding contact with the guide. As a result of the comparatively large distance between, on the one hand, positions of the guiding contact between the guiding element and the guide and, on the other hand, the optical component, viewed in the direction of the optical axis of the optical component, the risk of an oblique position of the optical component relative to the plane perpendicular to the optical axis is limited, and the optical component can be accurately positioned.
In accordance with a very special preferred embodiment, a resilient element is provided which, on one side, engages the holder and, on another opposite side, engages the frame so as to cause the guiding element and the guide to co-operate. Apart from optimum guidance, such a resilient element will ensure that once a position has been set, changes to this position, for example under the influence of shocks, that might lead to the optical system becoming deranged do not take place.
The resilient element preferably acts substantially mirror symmetrically with respect to the plane defined by the optical axis and the longitudinal axis of the guiding element, as a result of which a mechanically stable situation is obtained.
To increase the stability of the adjusting mechanism, the holder is preferably provided with a further guiding element, which can be guided along a further guide of the frame, which further guiding element co-operates with the further guide, at least partly under the influence of the resilient element. In this case, the further guiding element may form a tilt axis, said further guiding element then being held against the further guide by the resilient element because of the moment equilibrium.
It is particularly advantageous if the resilient element engages the holder substantially pointwise, resulting in the formation of a substantially frictionless hinged joint, which hinges during the adjusting of the optical component.
It has been found that an Omega-shaped resilient element is very advantageous, whereby the ends of the Omega shape act towards each other and, if the resilient element is provided with an inwardly directed bend at the two ends of the Omega shape, said ends engage pointwise.
To set the optical component, the holder is preferably provided with engaging means for co-operating with a tool used to set the optical component so as to be positioned in the direction of the optical axis. The engaging means can co-operate with external engaging means of said tool, said tool being, for example, pin-shaped or fork-shaped.
Preferably, the engaging means are provided near the guiding element, so that adjusting the optical component causes no, or a minimum of, moment loads on the holder, which could lead to an undesirable oblique position of the optical component.
These and other aspects of the invention will be apparent from and elucidated with reference to a preferred embodiment described hereinafter.